It is known to transfer the single sheets to a conveyor belt above which an electronic camera is provided for each row of cards. The cameras are connected with a computer which has a comparator circuit which compares the camera images with a criteria catalogue.
Sheets which have defective cards are sorted out, while sheets having flawless cards are conveyed for further processing.
If, for example, a sheet has eight rows of cards, then eight cameras are required for this monitoring device. However, cameras with a corresponding resolution are very expensive. A further disadvantage of the known device can be seen therein that sheets having only a few defective cards can also be rejected.